Method for measuring light intensity distribution

ABSTRACT

A method for measuring intensity distribution of light includes a step of providing a carbon nanotube array located on a surface of a substrate. The carbon nanotube array has a top surface away from the substrate. The carbon nanotube array with the substrate is located in an inertia environment or a vacuum environment. A light source irradiates the top surface of the carbon nanotube array, to make the carbon nanotube array radiate a visible light. A reflector is provided, and the visible light is reflected by the reflector. An imaging element images the visible light reflected by the reflector, to obtain an intensity distribution of the light source.

RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201210192083.X, filed on Jun. 12, 2012 inthe China Intellectual Property Office. This application is related tocommonly-assigned application entitled, “SYSTEM FOR MEASURING LIGHTINTENSITY DISTRIBUTION”, filed on Dec. 28, 2012, Ser. No. 13/729,279;“SYSTEM FOR MEASURING LIGHT INTENSITY DISTRIBUTION”, filed on Dec. 28,2012, Ser. No. 13/729,285; “METHOD FOR MEASURING LIGHT INTENSITYDISTRIBUTION”, filed on Dec. 28, 2012, Ser. No. 13/729,522. Disclosuresof the above-identified applications are incorporated herein byreference.

BACKGROUND

1. Technical Field

The present application relates to a method for measuring lightintensity distribution.

2. Discussion of Related Art

To measure an intensity distribution of a light source, a sensor is putin a position away from the light source in some related art. Then thesensor is moved around a circumference of a circle with the light sourceas a center of the circle. It is necessary to move the sensor to obtaina plurality of testing data while measuring the intensity distributionof a light source.

The sensors used in measuring intensity distribution of light source canbe classified into two types: thermal and photonic. The thermal sensorsare low-cost and can be operated at room temperature but have lowsensitivity and low response speed. The photonic sensors have highsensitivity and high response speed. However, the photonic sensors arehigh-cost and cannot be operated at room temperature.

What is needed, therefore, is to provide method of high sensitivity andhigh resolution for measuring intensity distribution of light at roomtemperature at a low-cost.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referencesto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a flowchart of one embodiment of a method for measuring lightintensity distribution.

FIG. 2 is a schematic view showing an optical path system of oneembodiment of the method for measuring light intensity distribution.

FIG. 3 shows a scanning electron microscope (SEM) image of a carbonnanotube array.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Referring to FIG. 1 and FIG. 2, a method for measuring light intensitydistribution of one embodiment includes the following steps:

(S1), making a carbon nanotube array 10 on a surface of a substrate 14,wherein the carbon nanotube array 10 has a top surface 102 away from thesubstrate 14;

(S2), placing the carbon nanotube array 10 with the substrate 14 in aninert gas environment or a vacuum environment;

(S3), irradiating the top surface 102 of the carbon nanotube array 10with a light source to make the carbon nanotube array 10 radiate avisible light;

(S4), placing a reflector 22 spaced from the carbon nanotube array 10,wherein the reflector 22 is adjacent to the top surface 102 of thecarbon nanotube array 10, and used to reflect the visible light; and

(S5), imaging the visible light reflected by the reflector 22 with animaging element 18 to obtain an intensity distribution of the lightsource.

In step (S1), a chemical vapor deposition process in one embodiment,fabricates the carbon nanotube array 10. The chemical vapor depositionprocess includes the steps of:

(S11), providing a substantially flat and smooth substrate 14, whereinthe substrate 14 can be a P-type silicon substrate, an N-type siliconsubstrate, or a silicon substrate having oxide layer disposed thereon.In one embodiment, the substrate 14 is a P-type silicon substrate havinga width of about 4 inches;

(S12), forming a catalyst on the surface of the substrate 14, whereinthe catalyst can be made of iron, cobalt, nickel, or any combinationalloy thereof;

(S13), annealing the substrate 14 with the catalyst at a temperatureranging from about 700° C. to about 900° C. in air for about 30 minutesto about 90 minutes;

(S14), heating the substrate 14 with the catalyst at a temperatureranging from about 500° C. to about 740° C. in a furnace with aprotective gas therein; and

(S15), supplying a carbon source gas to the furnace for about 5 minutesto about 30 minutes and growing the carbon nanotube array 10 on thesubstrate 14, wherein the carbon source gas may be hydrocarbon gas, suchas ethylene, methane, acetylene, ethane, or any combination thereof.

Moreover, the carbon nanotube array 10 formed under the above conditionsis essentially free of impurities such as carbonaceous or residualcatalyst particles.

In step (S1), the carbon nanotube array 10 includes a plurality ofcarbon nanotubes 12 substantially parallel to each other. The pluralityof carbon nanotubes 12 may be single-walled, double-walled, multi-walledcarbon nanotubes, or their combinations. The plurality of carbonnanotubes 12 which are single walled have a diameter of about 0.5nanometers (nm) to about 50 nm. The plurality of carbon nanotubes 12which are double walled have a diameter of about 1.0 nm to about 50 nm.The plurality of carbon nanotube 12 which are multi-walled have adiameter of about 1.5 nm to about 50 nm. The plurality of carbonnanotubes 12 has a height of about 100 nm to about 10 millimeters (mm),for example, the height of the plurality of carbon nanotubes 12 is 100microns, 500 microns, 1000 microns or 5 mm. In one embodiment, theplurality of carbon nanotubes 12 is multi-walled carbon nanotubes andhas a height of about 100 microns to about 1000 microns.

In step (S1), an angle between the plurality of carbon nanotubes 12 andthe surface of the substrate 14 can be in a range from about 10 degreesto about 90 degrees. In one embodiment, the angle between the pluralityof carbon nanotubes 12 and the surface of the substrate 14 is in a rangefrom about 60 degrees to about 90 degrees. Referring to FIG. 3, in oneembodiment, the plurality of carbon nanotubes 12 is perpendicular to thesurface of the substrate 14. An interspace between adjacent two of thecarbon nanotubes 12 can be in a range from about 0.1 nm to about 0.5 nm.The plurality of carbon nanotubes 12 includes a first end and a secondend opposite to the first end. The first ends of the plurality of carbonnanotubes 12 are away from the substrate 14, and the second ends of theplurality of carbon nanotubes 12 connect to the surface of the substrate14.

In step (S1), the plurality of carbon nanotubes 12 in the carbonnanotube array 10 is pressed using a compressing apparatus, to form theangle between the plurality of carbon nanotubes 12 and the surface ofthe substrate 14, wherein the angle is less than 90 degrees. In detail,a certain pressure can be applied to the carbon nanotube array 10 by thecompressing apparatus. In one embodiment, the compressing apparatus canbe a pressure head having a glossy surface. When a planar pressure headis used to press the carbon nanotube array along a pressing directionslanted to the surface of the substrate 14, the angle between theplurality of carbon nanotubes 12 and the surface of the substrate 14will be obtained. It is to be understood, the pressure and the pressingdirection can, opportunely, determine a size of the angle between theplurality of carbon nanotubes 12 and the surface of the substrate 14.

The carbon nanotube array 10 can be transferred from the substrate 14 toother bases. The plurality of carbon nanotubes 12 in the carbon nanotubearray 10 is parallel to each other when the carbon nanotube array 10 isseparated from the surface of the substrate 14 and located on otherbases. An angle between the plurality of carbon nanotubes 12 and asurface of other bases can be still in a range from about 10 degrees toabout 90 degrees. Other bases can be made of opaque materials, such asmetal, ceramic or resin.

In step (S2), the carbon nanotube array 10 with the substrate 14 can belocated in a chamber 20. The chamber 20 is made of light-transparentmaterials, such as glass, resin or zinc selenide (ZnSe). The chamber 20can be filled with nitrogen, ammonia or inertia gas. In anotherembodiment, a pressure in the chamber 20 can be in a range from about10⁻⁹ Pa to about 10⁻³ Pa.

In step (S3), the carbon nanotube array 10 has the top surface 102 and abottom surface 104 opposite to the top surface 102. Each of theplurality of carbon nanotubes 12 has a top end 122 and a bottom end 124opposite to the top end 122. The top end 122 of each of the carbonnanotubes 12 is close to the light source. The bottom end 124 of each ofthe carbon nanotubes 12 is away from the light source and connects tothe substrate 14. Each of the carbon nanotubes 12 orients along adirection from the bottom surface 104 to the top surface 102 of thecarbon nanotube array 10.

The light source can be infrared light, ultraviolet light. In oneembodiment, an infrared light is used as the light source.

An irradiating angle of the light source can be selected according toneed, which is between a light beam 16 from the light source and the topsurface 102 of the carbon nanotube array 10. In one embodiment, theirradiating angle is 90 degrees such that the light beam 16 issubstantially vertical to the top surface 102 of the carbon nanotubearray 10 and parallel to an axis of each of the carbon nanotubes 12.

While irradiating the top surface 102 of the carbon nanotube array 10with the light beam 16, the top surface 102 of the carbon nanotube array10 absorbs photons of the light source and produces heat, due to carbonnanotube array 10 having an ideal black body structure. The higher theintensity of the light source, the more photons that are absorbed by thetop surface 102 of the carbon nanotube array 10, the more heat will beproduced by the top surface 102. The plurality of carbon nanotubes 12has evidently heat conduction anisotropy. Heat is conducted along theaxes of the plurality of carbon nanotubes 12 and is hardly conductedalong a direction vertical to the axes of the plurality of carbonnanotubes 12. Therefore, the heat of each of the plurality of carbonnanotubes 12 has been conducted along a direction from the top end 122to the bottom end 124, until each of the plurality of carbon nanotubes12 has equal and uniform heat. Meanwhile, the carbon nanotube array 10radiates the visible light, due to carbon nanotube array 10 having anideal black body structure.

In detail, when the light beam 16 irradiates the top surface 102 of thecarbon nanotube array 10, for example, a light with a higher lightintensity in the light beam 16 irradiates a top end 122 of a carbonnanotube 12A. The top end 122 of the carbon nanotube 12A absorbs photonsof the light source and produces more heat. The heat is conducted alongthe direction from the top end 122 to the bottom end 124, until thecarbon nanotube 12A has equal and uniform heat. A light with a lowerlight intensity in the light beam 16 irradiates a top end 122 of acarbon nanotube 12B. The top end 122 of the carbon nanotube 12B absorbsphotons of the light source and produces less heat. The heat isconducted along the direction from the top end 122 to the bottom end124, until the carbon nanotube 12B has equal and uniform heat. Heat ofthe carbon nanotube 12A is more than heat of the carbon nanotube 12B.Meanwhile, the carbon nanotubes 12A and 12B radiate the visible lights,due to the plurality of carbon nanotubes 12 having an ideal black bodystructure. Therefore, a light intensity of the visible light radiated bythe carbon nanotubes 12A is higher than a light intensity of the visiblelight radiated by the carbon nanotubes 12B.

Light intensity of the visible light radiated by each of the pluralityof carbon nanotubes 12 in the carbon nanotube array 10 is related tolight intensity of the light source. The higher the intensity of thevisible light radiated by one of the plurality of carbon nanotubes 12,the more heat will be produced by the top end 122 of the plurality ofcarbon nanotubes 12, the higher the intensity of one light irradiatingthe top end 122 of the plurality of carbon nanotubes 12.

The substrate 14 is made of silicon which is opaque. The bottom surface104 of the carbon nanotube array 10 connects to the substrate 14.Therefore, visible light radiated by the bottom of the carbon nanotubearray 10 is turned back by the substrate 14.

In step (S4), the plurality of carbon nanotubes 12 have evidently heatconduction anisotropy. Heat is conducted along the axes of the pluralityof carbon nanotubes 12 and is hardly conducted along a directionvertical to the axes of the plurality of carbon nanotubes 12. Therefore,when the carbon nanotube array 10 radiates visible light, the topsurface 102 and the bottom surface 104 of the carbon nanotube array 10radiates more visible light. Side surfaces of the carbon nanotube array10 hardly radiate visible light, wherein the side surface is parallel tothe axes of the plurality of carbon nanotubes 12. Only the top surface102 radiates the visible light, because the visible light radiated bythe bottom surface 104 is turned back by the opaque substrate 14. Thereflector 22 is adjacent to the top surface 102 of the carbon nanotubearray 10 and spaces from the carbon nanotube array 10. In not affectingaberration case, a distance between the reflector 22 and the carbonnanotube array 10 can be less than 80 mm, allowing the top surface 102to irradiate more visible light. In one embodiment, a center of the topsurface 102 of the carbon nanotube array 10 is located in a focus of thereflector 22.

A curvature radius of the reflector 22 can be in a range from about 10mm to about 100 mm, to obtain more visible light. In one embodiment, thecurvature radius of the reflector 22 is 88 mm, an object aperture angleof the reflector 22 is greater than or equal to 22.5 degrees, anumerical aperture of the reflector 22 is greater than 0.38.

In step (S5), the imaging element 18 can be a charge-coupled device(CCD), a complementary metal-oxide-semiconductor (CMOS). In oneembodiment, the imaging element 18 is a CCD, a size of a picture elementof the CCD is less than 10 microns. In one embodiment, the chamber 20spaced from the imaging element 18 and the reflector 22 is locatedbetween the imaging element 18 and the reflector 22. The carbon nanotubearray 10 is located between the substrate 14 and the reflector 22. Thesubstrate 14 is located between the carbon nanotube array 10 and theimaging element 18.

A size of the imaging element 18 is related to the curvature radius ofthe reflector 22. In one embodiment, the size of the imaging element 18is 8.47 mm, a height of the image is 3.8 mm. A diameter of a imagedefocused spot is less than 0.01 mm, 0.7 view field distortion is lessthan or equal to 1%, field region is less than 0.01 mm, an opticaltransfer function in 50 line pairs/mm is great than 0.8. The method formeasuring light intensity distribution can distinguish detail which hasa size of great than or equal to 10 microns.

After imaging the visible light reflected by the reflector 22 with theimaging element 18, the intensity distribution of the light source canbe obtained by reading the imaging element 18. A computer can be usedfor reading the imaging element 18 to obtain the intensity distributionof the light source.

In summary, the method for measuring intensity distribution of light canbe at room temperature. The method for measuring intensity distributionof light has higher sensitive and resolution, and can distinguish detailwhich has a size of greater than or equal to 10 microns. Moreover, themethod for measuring intensity distribution of light is simple and easyto implement.

It is to be understood that the above-described embodiment is intendedto illustrate rather than limit the disclosure. Variations may be madeto the embodiment without departing from the spirit of the disclosure asclaimed. The above-described embodiments are intended to illustrate thescope of the disclosure and not restricted to the scope of thedisclosure.

It is also to be understood that the above description and the claimsdrawn to a method may include some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

What is claimed is:
 1. A method for measuring intensity distribution of light comprising: (S1) making a carbon nanotube array comprising a plurality of carbon nanotubes on a surface of a substrate, wherein the carbon nanotube array comprises a top surface away from the substrate; (S2) placing the carbon nanotube array with the substrate in an inert gas environment or a vacuum environment; (S3) irradiating the top surface of the carbon nanotube array with a light source to make the carbon nanotube array radiate a visible light and the angles between the plurality of carbon nanotubes and the surface of the substrate are in the range from about 10 degrees to 90 degrees; (S4) placing a reflector to reflect the visible light; and (S5) imaging the visible light reflected by the reflector with an imaging element to obtain an intensity distribution of the light source.
 2. The method of claim 1, wherein the carbon nanotube array comprises a plurality of carbon nanotubes parallel to each other.
 3. The method of claim 2, wherein in the step (S3), the top surface of the carbon nanotube arrays is irradiated at an irradiating angle of 90 degrees, the irradiating angle is defined between a light beam from the light source and the top surface of the carbon nanotube array.
 4. The method of claim 3, wherein the light beam is substantially vertical to the top surface of the carbon nanotube array and parallel to axes of the plurality of carbon nanotubes.
 5. The method of claim 1, wherein in the step (S1), the carbon nanotube array is manufactured by the steps of: (S11) providing a substrate which is substantially flat and smooth; (S12) forming a catalyst on the substrate; (S13) annealing the substrate with the catalyst at a temperature ranging from about 700° C. to about 900° C. in air for about 30 minutes to about 90 minutes; (S14) heating the substrate with the catalyst at a temperature ranging from about 500° C. to about 740° C. in a furnace with a protective gas therein; and (S15) supplying a carbon source gas to the furnace for about 5 minutes to about 30 minutes and growing the carbon nanotube array on the substrate.
 6. The method of claim 1, wherein the angles between the plurality of carbon nanotubes and the surface of the substrate are in a range from about 60 degrees to about 90 degrees.
 7. The method of claim 1, the step (S1) further comprises pressing the plurality of carbon nanotubes by a compressing apparatus to form the angles between the plurality of carbon nanotubes and the surface of the substrate.
 8. The method of claim 1, wherein the substrate is made of opaque materials.
 9. The method of claim 1, wherein in the step (S2), the carbon nanotube array with the substrate is placed in a chamber made of light-transparent materials.
 10. The method of claim 9, wherein the chamber is filled with nitrogen, ammonia or inert gas.
 11. The method of claim 9, wherein a pressure in the chamber is in a range from about 10⁻⁹ Pa to about 10⁻³ Pa.
 12. The method of claim 9, the step (S2) further comprises separating the chamber from the imaging element and the reflector and placing the chamber between the imaging element and the reflector.
 13. The method of claim 1, wherein the light source is infrared light or ultraviolet light.
 14. The method of claim 1, wherein in the step (S4), the reflector is placed at a distance between the reflector and the carbon nanotube array less than 80 millimeters.
 15. The method of claim 1, wherein in the step (S4), a focus point of the reflector is placed at a center of the top surface of the carbon nanotube array.
 16. The method of claim 1, wherein a curvature radius of the reflector is in a range from about 10 millimeters to about 100 millimeters.
 17. The method of claim 1, wherein in the step (S4), the reflector is placed separated from the carbon nanotube array and adjacent to the top surface of the carbon nanotube array.
 18. The method of claim 1, wherein the step (S2) comprises placing the carbon nanotube array and the substrate such that the substrate is between the carbon nanotube array and imaging element.
 19. The method of claim 1, wherein the imaging element is a charge-coupled device or a complementary metal-oxide-semiconductor. 